Transmission of pathogens through tick vectors results in different infectious diseases in humans with Lyme disease affecting most people in the United States and Europe. Ticks can infect people with disease-causing organisms, including three different species of the Lyme spirochetes Borrelia burgdorferi, B. afzelii, and B. garinii, the intracellular bacterial pathogen Anaplasma phagocytophilum, and the protozoan Babesia microti and other Babesia species. Major species implicated in causing Lyme disease are Borrelia burgdorferi sensu stricto in the USA and additionally, B. afzelii and B. garinii in the European countries. Co-infection of Borrelia species with two other pathogens, A. phagocytophilum and Babesia species, has started appearing in both North America and Europe. Babesia species infect red blood cells (erythrocytes), cause babesiosis, and can also be transmitted through blood transfusion. Recently, several cases of vertical transmission of B. microti have also been reported. A. phagocytophilum infects polymorphonuclear leukocytes (PMNs), is an obligate intracellular pathogen and can cause lymphopenia/leukopenia and thrombocytopenia resulting in human granulocytic anaplasmosis (HGA). Both babesiosis and HGA can be fatal.
Currently, serological tests are used primarily to diagnose all three diseases with culture as the only available confirmatory test. However, assays that detect antibodies do not detect early infections (before antibodies are produced), and they cannot distinguish between active infections and infections that have been cured by treatment (as antibodies persist long after treatment is completed). Nucleic acid-based assays, on the other hand, are able to specifically detect the presence of the pathogens that cause Lyme disease and other tick-borne diseases. Yet, current assays that detect specific nucleic acid sequences are insufficiently multiplex to provide an accurate picture as to whether one or more of the infectious pathogens were introduced by the ticks during the bloodmeal. Furthermore, simultaneous infection with more than one pathogen can affect the sensitivity of currently available tests.
Sensitive diagnostic tests that can accurately diagnose Lyme disease, anaplasmosis and babesiosis are not currently available, thus, emphasizing a need to develop individual test for each pathogen or a combinatorial test for all three tick-borne pathogens to detect co-infection. Thus, there is a desperate need to develop a technically simple, rapid and accurate assay to unequivocally diagnose active disease caused by these three tick-borne infections, individually or together.